I. Field of the Invention
The present invention relates generally to antennas and, more specifically, to a folded quarter-wave patch antenna.
II. Description of the Related Art
Antennas are an important component of wireless communication system. Although antennas may seem to be available in numerous different shapes and sizes, they all operate according to the same basic principles of electromagnetics. An antenna is a structure associated with a region of transition between a guided wave and a free-space wave, or vice versa. As a general principle, a guided wave traveling along a transmission line which opens out will radiate as a free-space wave, also known as an electromagnetic wave.
In recent years, with the increase in use of personal communication devices, such as cellular hand-held and mobile phones and PCS phones, the need for small antennas that are suitable for use in personal communication devices has increased. Recent developments in integrated circuits and battery technology have enabled the size and weight of the communication devices to be reduced drastically over the past several years. One area in which reduction in size is still desired is the communication device's antenna. This is due to the fact that the size of the antenna play an important role in decreasing the size of the device. In addition, the antenna size and shape impact the device aesthetics and manufacturing costs.
An important factor to be considered in designing antennas for personal communication devices is the radiation pattern. In a typical application, the communication device must be able to communicate with another user or a base station or hub which can be located in any number of directions from the user. Consequently, in personal communication devices, it is essential that the antenna has an omnidirectional radiation pattern.
One antenna commonly used in personal communication devices is the whip antenna. There are, however, several disadvantages associated with the whip antenna. Often, the whip antenna is subject to damage by catching on things. Even when the whip antenna is designed to be retractable in order to prevent such damage, it consumes scarce interior space. This results in less interior space being available for advanced features and circuits. Also, as personal communication devices such as cellular phones become smaller, the ability to use the whip antenna efficiently is being challenged.
Another antenna which may also be suitable for use in personal communication devices is the patch or microstrip antenna. The patch antenna was originally developed in the late 1960's for use with aircraft, missiles and other military applications requiring a paper thin or low-profile antenna. These applications required that the antenna neither disturb the aerodynamic flow nor protrude inwardly to disrupt the mechanical structure. The patch antenna satisfied these requirements.
As its name suggests, the patch antenna includes a patch or a conductor plate. The length of the patch is set in relation to the wavelength .lambda..sub.0 associated with the resonant frequency f.sub.0. When the length of the patch is set at .lambda./.sub.4, the antenna is known as a quarter-wave patch antenna.
Unfortunately, currently available patch antennas are generally too large for use in personal communication devices. A reduction in the length of the patch antenna would make it increasingly desirable for use in personal communication devices. For example, a reduction in the length of the patch antenna would make the personal communication device more compact and aesthetic.